Metallic articles are fabricated by any of a number of techniques, as may be appropriate for the nature of the metal and the article. In one common approach, metal-containing ores are refined to produce a molten metal, which is thereafter cast. The metal is refined as necessary to remove or reduce the amounts of undesirable minor elements. The composition of the refined metal is usually modified by the addition of desirable alloying constituents. These refining and alloying steps may be performed during the initial melting process or after solidification and remelting. After a metal of the desired composition is produced, it may be used in the as-cast form for some alloy compositions (i.e., cast alloys), or further mechanically worked to form the metal to the desired shape for other alloy compositions (i.e., wrought alloys), or processed through another physical form (i.e., powder which is thereafter consolidated). In these approaches, further processing such as heat treating, machining, surface coating, and the like may also be employed.
Some metallic alloys arc relatively straightforward to produce by this general approach. The alloying elements are thermophysically compatible in the molten state, so that the alloys may be produced by melting and processing. However, in the subsequent processing operations complications may develop. The cast or cast-and-worked alloys may exhibit irregularities in macrostructure and microstructure that interfere with the realization of the potential properties of the alloys. For example, there may be extensive defect structures, there may be chemical inhomogeneities, there may be a tendency to cracking that reduces the fatigue life of the final product, it may not be possible to inspect the product sufficiently, and/or the grain size may be too large to impart the desired properties. The costs of production may be high and prohibitive for some applications.
The production of other metallic alloys is complicated in many cases by the differences in the thermophysical properties of the elemental metallic constituents being combined to produce the alloy. The interactions and reactions due to these thermophysical properties of the metallic constituents may cause undesirable results. In one commercially important example, titanium alloys must be melted in a vacuum because of their reactivity with oxygen and nitrogen in the air. In the work leading to the present invention, the inventors have realized that the necessity to melt under a vacuum makes it difficult to utilize some desirable alloying elements due to the differences in their relative vapor pressures in a vacuum environment. The difference in the vapor pressures is one of the thermophysical properties that must be considered in alloying titanium. In other cases, the metallic alloying constituents may be thermophysically incompatible with the molten titanium because of other thermophysical characteristics such as melting points, liquid-phase immiscibility, densities, chemical reactivities and the tendency of strong beta stabilizers to segregate. Some of the incompatibilities may be overcome with the use of expensive master alloys, but this approach is not applicable in other cases. And even where the thermophysical incompatibilities are overcome, there may be difficulty in achieving homogeneity in the alloys due to the manner of melting.
Thus, there is a need for an improved approach to producing alloys of titanium and other metals, with added metallic alloying constituents. The need extends both to conventional meltable alloys, where macrostructural and microstructural limitations must be overcome, and non-meltable alloys, in which the previous alloying limitations are overcome and the alloys may be made highly homogeneous. The present invention fulfills this need, and further provides related advantages.